// Copyright 2024 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package internal

import (
	"context"
	"net/http"
	"sync/atomic"
	"time"
)

// RequestInfo is information about an HTTP request.
type RequestInfo struct {
	Request    *http.Request
	TrimmedURL string       // URL with the scheme and host removed
	TraceID    string       // extracted from request header
	Start      time.Time    // when the request began
	State      atomic.Value // string describing current state; see [RequestState]
	Cancel     func(error)  // function that cancels the request's context
}

func NewRequestInfo(r *http.Request) *RequestInfo {
	turl := *r.URL
	turl.Scheme = ""
	turl.Host = ""
	turl.User = nil
	ri := &RequestInfo{
		Request:    r,
		TrimmedURL: turl.String(),
		TraceID:    r.Header.Get("X-Cloud-Trace-Context"),
		Start:      time.Now(),
	}
	ri.State.Store("")
	return ri
}

// requestInfoKey is the type of the context key for RequestInfos.
type requestInfoKey struct{}

// NewContextWithRequestInfo creates a new context from ctx that adds the trace ID.
func NewContextWithRequestInfo(ctx context.Context, ri *RequestInfo) context.Context {
	return context.WithValue(ctx, requestInfoKey{}, ri)
}

// RequestInfoFromContext retrieves the trace ID from the context, or a zero one
// if it isn't there.
func RequestInfoFromContext(ctx context.Context) *RequestInfo {
	ri, _ := ctx.Value(requestInfoKey{}).(*RequestInfo)
	if ri == nil {
		return &RequestInfo{}
	}
	return ri
}

// RequestState sets the State field of the current request.
// It returns a function that restores the value of the field.
// Typical use:
//
//	defer RequestState(ctx, "frobbing")()
func RequestState(ctx context.Context, s string) func() {
	ri := RequestInfoFromContext(ctx)
	old := ri.State.Load()
	if old == nil {
		// This RequestInfo was not initialized with NewRequestInfo.
		// It is the zero value returned by RequestInfoFromContext
		// when there is no RequestInfo in the context. Do nothing in this case.
		return func() {}
	}
	ri.State.Store(s)
	return func() { ri.State.Store(old) }
}